IRE1/XBP1s signaling: a novel essential regulator for bone marrow microenvironmen

描述（由申请人提供）：多发性骨髓瘤（MM）是最常见的累及骨骼的癌症，在轴骨和颅面骨中诱发溶骨性病变，这种病变很少愈合。多发性骨髓瘤骨病（MMBD）是MM的一些最具破坏性的并发症的原因，也是MM相关发病率的主要来源。骨髓基质细胞（BMSC）是MM微环境中存在的主要细胞类型。研究表明，在MMBD中，BMSC产生许多生长因子和炎症细胞因子。这些因素可以促进骨髓瘤肿瘤细胞的生长，激活破骨细胞（骨吸收细胞），诱发骨溶解病变。因此，破坏骨髓间充质干细胞对MM细胞生长和破骨细胞形成的支持对治疗MMBD具有重要的临床意义。我们的长期目标是阐明调节骨髓间充质干细胞支持MMBD中MM细胞生长和骨破坏的分子机制，并确定破坏骨髓间充质干细胞支持MMBD的潜在治疗靶点。为了实现这一目标，我们发现，与来自健康供者的骨髓间充质干细胞相比，来自MM患者的骨髓间充质干细胞诱导了一种细胞应激分子剪接的x- box结合蛋白1 （XBP1s）。XBP1s已被证明在其他器官和疾病模型（如炎症性肠病）中控制炎症细胞因子的基因表达和/或蛋白质分泌。我们最近发现，在健康供体骨髓间充质干细胞中，XBP1s蛋白水平的升高诱导了通常存在于MM患者骨髓间充质干细胞中的病理行为，如炎症细胞因子分泌增加，体外和体内对MM细胞生长和OCL形成的支持增强。相反，MM患者BMSC中xbp1的敲低在很大程度上将其病理行为纠正到与健康供体BMSC相当的水平。在这项RO1拨款申请中，我们假设IRE1α/XBP1s信号是调节骨髓间充质干细胞炎症特征和骨髓间充质干细胞支持MM细胞生长和破骨细胞发生的重要病理生理因子。因此，骨髓间充质干细胞中的IRE1/XBP1s信号是一个潜在的治疗靶点，可以破坏骨髓间充质干细胞对MM细胞生长和骨破坏的支持，从而治疗MMBD。具体目标是：

DESCRIPTION (provided by applicant): Multiple myeloma (MM) is the most frequent cancer to involve the skeleton and induces osteolytic lesions that rarely heal in both axial and craniofacial bones. Multiple myeloma bone disease (MMBD) is responsible for some of the most devastating complications of MM and is the major source of morbidity associated with MM. Bone marrow stromal cells (BMSC) are a major type of cells that reside within the MM microenvironment. It has been shown that in MMBD, BMSC produce many growth factors and inflammatory cytokines. These factors can boost the growth of the myeloma tumor cells and activate osteoclasts, the bone resorbing cells, to induce osteolytic lesions in bone. Thus, disrupting the BMSC support of MM cell growth and osteoclast formation is of major clinical significance in treating MMBD. Our long-term goal is to elucidate the molecular mechanisms that regulate BMSC support of MM cell growth and bone destruction in MMBD and identify the potential therapeutic targets for disrupting BMSC support of MMBD. Towards this goal, we have found that a cellular stress molecule spliced X-box-binding protein 1 (XBP1s) is induced in the BMSC derived from MM patients, compared with those from the healthy donors. XBP1s has been shown to control gene expression and/or protein secretion of inflammatory cytokines in other organs and disease models, such as inflammatory bowel disease. We showed recently that elevation of XBP1s protein levels in healthy donor BMSC induced the pathological behavior that are usually present in MM patient BMSCs, such as, heightened inflammatory cytokine secretion, enhanced support of MM cell growth and OCL formation both in vitro and in vivo. Conversely, knockdown of XBP1s in MM patient BMSC largely corrected their pathological behavior to the levels that are comparable to healthy donor BMSC. In this RO1 grant application, we hypothesize that IRE1α/XBP1s signaling is an essential pathophysiological factor that regulates the BMSC inflammatory signature and BMSC support of MM cell growth and osteoclastogenesis. Thus, the IRE1/XBP1s signaling in BMSC is a potential therapeutic target for disrupting BMSC support of MM cell growth and bone destruction in treating MMBD. The Specific Aims are: Aim 1: To determine the pathophysiological significance of p38-induced phosphorylation of human XBP1s (hXBP1s) in BMSC support of MM cell growth and osteoclastogenesis both in vitro and in vivo. Aim 2: To determine whether RANKL is a novel transcriptional target of XBP1s. Aim 3: To determine whether deletion of Xbp1 in BMSC blunts MM cell growth and bone resorption in vivo using a novel immunocompetent BMSC-specific Xbp1 KO mouse model. Aim 4: To determine if the IRE1α endoribonuclease activity in BMSC represents a potential therapeutic target to repress generation of XBP1s and disrupt BMSC support of MM cell growth and OCL formation. These studies have multiple biological, pathological and clinical implications. First, our studies will provide important information and related animal models for developing and employing therapeutic strategies that target the IRE1α/XBP1s signaling, such as the existing IRE1α inhibitors, and/or inflammation kinases-induced phosphorylation of XBP1s to disrupt the protective effects of the MM microenvironment on MM cells and OCL as a means to treat MMBD. Secondly, these studies will not only advance our understanding of basic biology of XBP1s but also provide important information on potential impact of an IRE1α/XBP1s inhibitor on bone microenvironment homeostasis of MM patients. Thirdly, since heightened stromal inflammatory cytokine secretion is a common pathological feature of many inflammatory bone diseases, such as rheumatoid osteoarthritis and tumor bone metastases (e.g., prostate, breast and lung cancers), our studies will provide important information and related animal models to investigate if the IRE1α/XBP1s signaling in BMSC is also a critical pathological factor in regulating the stromal cells support of progress of these inflammatory bone diseases, and thus represents a potential therapeutic targets for treating these inflammatory bone diseases.